How to make IMAPS SSL Cert for Dovecot that works with Thunderbird

[hanas...@gmail.com]

Hello all,

What are the instructions for making an SSL cert for Dovecot IMAPS?
Two methods have been tried, and work, with Evolution; however generate 
the following error when Thunderbird tries to connect.

Thank you,

method 1 : self signed
openssl req -newkey rsa:4096 -sha512 -x509 -days 365 -nodes -keyout 
mykey.key -out mycert.pem

method 2 : Let's Encrypt (LE) CA
Created with Certbot

ERROR
 TLS handshaking: SSL_accept() failed: error:14094412:SSL 
routines:ssl3_read_bytes:sslv3 alert bad certificate: SSL alert number 
42, session=<+oooooo>
<<attachment: hanasaki.vcf>>